The invention relates to an apparatus for determining the path of a pulsed light beam passing through an air space, which apparatus comprises a light sensitive detector system in a measuring station situated on the side of the beam path.
Such an apparatus is known from the published British patent application No. 2.151.871. In this case the light sensitive detector system has a number of fixed sensitive lobes at known angular distances relative to each other, whilst at least three of these lobes must be directed towards the beam path to be determined. When a light pulse passes in its path through these three sensitive lobes, the light sensitive detector system will receive pulses of scattered radiation in successive order in the three sensitive lobes. A time measuring circuit connected to the detector device measures the moments of arrival for the scattered light in the three lobes and determines the mutual time distance between these moments of arrival. The time difference depends upon differences in travelling distance in the three lobes, on the one hand for the light pulse itself causing the scattered radiation and on the other hand for the scattered radiation, at the reception of this scattered radiation in the three lobes. These travelling distance differences are caused by geometrical conditions and can be expressed in simple geometrical relationships comprising the known lobe directions and two variables, which describe the unknown beam path. By means of at least two measured time distances the beam path can be determined with the use of these relationships.
A characteristic property of this apparatus is that it can determine the path for one single light pulse, provided that the scattered radiation from the light pulse can be intercepted by the detector device via at least three lobes. It can therefore be used for measuring the path also for distance laser devices, which in principle need only transmit one single pulse to have full information about the desired distance.
A drawback of the known apparatus is that the detector system is complicated and expensive if it is to cover a large part of the space, for example 360.degree. .In spite of this in a practical embodiment of the device it may only be ensured that scattered radiation can be detected via the requried minimum of three lobes. This may involve low accuracy of determining the path.